Forced circulation electric heater employing cross-flow type fan



Feb. 21, 1967 N LAING 3,305,665

FORCED CIRCULA TION ELECTRIC HEATER EMPLOYING CROSS-FLOW TYPE FANOriginal Filed Nov. 17, 1959 5 Sheets-Sheet l /4 45 9 FIG].- MMMMMMMMMMMIMI l Feb. 21, 1967 LAlNG 3305,665

FORCED CIRCULATION ELECTRIC HEATER EMPLOYING CROSS-FLOW TYPE FANOriginal Filed Nov. 17. 1959 5 Sheets-Sheet 2 Feb. 21, 1967 LAING3,305,665

FORCED CIRCULATION ELECTRIC HEATER EMPLOYING CROSS-FLOW TYPE FANOriginal Filed Nov. 17, 1959 5 Sheets-Sheet 3 Feb. 21, 196/ N. LAlNG3,305,665

FORGED CIRCULATION ELECTRIC HEATER EMPLOYING CROSS-FLOW TYPE FANOriginal Filed Nov. 17, 1959 5 Sheets-Sheet 4 Feb. 21, 1967 LAlNG3,305,665

N. FORCED CIRCULATION ELECTRIC HEATER EMPLOYING CROSS-FLOW TYPE FANOriginal Filed Nov. 17. 1959 5 Sheets-Sheet 5 United States Patent47as0s 1 Claim. (Cl. 219-370 This invention relates to fans of thecross-flow type. The application is a division of my copendingapplication Serial No. 853,596 filed November 17, 1959, now abandoned.

The invention more particularly concerns fans of the cross-flow type,that is, machines comprising a cylindrical bladed rotor mounted forrotation about its axis in a predetermined direction and defining aninterior space, and guide means defining with the rotor an entry regionand a discharge region, the guide means and rotor cooperating onrotation of the latter in said predetermined direction to induce a flowof air from the entry region through the path of the rotating blades ofthe rotor to said interior space and thence again through the path ofsaid rotating blades to the discharge region. More especially but notexclusively, the invention concerns fans of the cross-flow type whereinthe guide means and rotor cooperate to set up a vortex of Rankinecharacter having a core region eccentric of the rotor axis and a fieldregion which guides the air so that flow through the rotor is stronglycurved about the vortex core: such fans are sometimes known astangential fans and the preferred form of fan to be described in detaillater is of this type.

The invention is more especially concerned with fan heaters employingcross-flow fans. A cross-flow fan heater according to the invention hasguide means in the form of a pair of end walls in substantial alignmentwith the ends of the rotor and a pair of guide walls, these wallsdefining a discharge duct mounting heater means, generally, but notnecessarily, an electric resistance element extending within the duct.

The cross-flow fan is relatively compact and capable of passing arelatively large volume of air through the discharge duct, which cantake up a correspondingly large amount of heat. On the other hand it isgenerally undesirable, especially in a domestic heater, for the heatingmeans to reach an excessive temperature. In one aspect of the inventionthe heater means is mounted on the discharge duct to extend at an angleto the direction of air flow therethrough, so as to extend over agreater area than the cross-sectional area of the duct takenperpendicularly to the flow direction. The discharge duct is moreoverpreferably divergent in the direction of flow, which has the twineifects of increasing the static pressure of the air to overcome suchresistance to flow as the heating means may oiIer, and increasingfurther the area which the heating means may occupy. These measuresallow the designer relative freedom to provide for substantial heatingof the air fiow with a relatively cool heating means. The spacing andarrangement of the resistance wire, if such is used, has been found tomake a considerable difference to the resistance to flow and theturbulence of the emergent jet, as will be explained. The arrangement ofthe heating means as just described gives scope to dispose theresistance wire or its equivalent to the best advantage.

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In a further aspect of the invention, the heating means is mounted formovement between a retracted position wherein air flow through thedischarge duct is unobstructed by the heater means and an operativeposition wherein the heater means is located in the path of said airflow. This is particularly advantageous if the fan has to operate forperiods without the heater e.g. for air circulation purposes in summer.

The tangential fan as above defined tends to produce in the outlet ducta flow which is faster adjacent one guide wall than adjacent the other,due to the fact that the flow in the vortex field is faster near thecore than remote from it. In one aspect of the invention based on thisrealization, the heating element has resistance wires more closelyspaced adjacent this one wall where the flow is faster than adjacent theother wall.

In a further aspect of the invention the ends of the rotor are receivedin recesses in the end walls so that adjacent these walls the air canflow more smoothly.

The invention will be further described with reference to theaccompanying somewhat diagrammatic drawings illustrating, by way ofexample only, various embodiments of the invention. In the drawings:

FIGURE 1 shows in vertical section one form of crossflow fan heateraccording to the invention;

FIGURE 2 is a partly cut-away horizontal section of the FIGURE 1 fanheater showing certain parts in plan view;

FIGURE 3 is a vertical section of a second embodiment of a cross flowfan heater according to the invention;

FIGURE 4 is a vertical section of a third embodiment of part of a crossflow fan heater constructed according to the invention;

FIGURE 5 is a vertical section of a fourth embodiment of part of a crossflow fan heater constructed according to the invention;

FIGURE 6 is a vertical section of a fifth embodiment of part of a crossflow fan heater constructed according to the invention;

FIGURE 7 is a vertical section of a sixth embodiment of part of a crossfiow fan heater constructed according to the invention;

FIGURE 8 is a vertical section of a seventh embodiment of part of across flow fan heater constructed according to the invention;

FIGURES 9a, 9b and show schematically the effect of diiferent conditionson the turbulence of flow past a resistance wire, and

FIGURE 10 is a sectional view illustrating mounting arrangements for theFIGURE 1 rotor.

Referring to the drawings, the fan heater illustrated in FIGURES 1 and 2thereof comprises a casing 1 enclosing a cross-flow fan unit comprisinga rotatably mounted cylindrical bladed rotor 2 and a pair of guide walls3, 4 interconnected by parallel end walls 5, 6 all these walls 3, 4, 5,6 being held spaced from the interior of the casing. The casing 1 hasend walls 7, 8 and top and bottom Walls 9, 10, a vertical left hand wall11 (as viewed in FIGURES 1 and 2) and an upwardly and outwardly slopingright hand wall 12: a sloping wall portion 13 joins the lower edge ofthe wall 11 to the bottom wall 18*, while the top wall 9 slopes down atthe right hand side to point the upper edge of the Wall 12; in anyhorizontal cross-section the casing has a rectangular outline. An airinlet 14 to the casing 1 is provided over adjacent areas of the sidewall 11 and top wall 9 which lie opposite the rotor 2. An air outlet 15is provided over an area of the side wall 12 opposite the rotor 2.Curved vanes 16, 17 extend longitudinally across inlet and outlet 14, 15to prevent manual contact respectively with the rotor 2 and with heatermeans to be described.

The casing 1 provides on the inside of the end wall 7 aninwardly-opening recess 18 snugly receiving and locating a fractionalhorsepower electric motor 19 the shaft 20 of which supports one end ofthe rotor 2 and drives it in the direction of the arrow 21. At thebottom of the recess 18 the end wall 7 is perforated at 22 for access ofcooling air to the motor 19.

The guide walls 3, 4 which extend the length of the rotor 2, each have amain portion 25, 26 and an outlet guide portion 27, 28. The main guideportions 25, 26 of the guide walls face each other across the rotor 2and are spaced therefrom an appreciable distance at their lines ofnearest approach thereto, designated 30, 31 which define a nearly 180arc of air entry to the rotor. In the example shown, the main guideportion 25 converges With the rotor in the direction of rotor rotationshown by the arrow 21. The outlet guide portions 27, 28 of the guidewalls 3, 4 are straight and diverge in the direction of flow to form anoutlet duct 32, in this embodiment acting as a diffuser and dischargingdirectly towards the outlet 15. The main guide and outlet portions 25,27 of the guide wall 3 meet in a nose 33 and define thereat an angle ofjust over a right angle. The main guide and outlet portions 26, 28 ofthe wall 4 merge in a smooth surface diverging steadily from the line 31of nearest approach to the rotor. The wall 3 includes a lead-in portion34 guiding air to the rotor 2. The edges of the guide walls 3, 4terminate in spaced relation to the casing 1 adjacent the inlet 14 andoutlet 15.

In operation, the rotor 2 and guide walls 3, 4 cooperate to set upvortex having, adjacent the wall 3, a generally cylindrical coreparallel to and eccentric of the rotor axis and interpenetrating therotor blades. This vortex core is a rotating body of air and theoutermost, and fastest, stream tube thereofis diagrammatically indicatedat V in FIGURE 1. By reason of the vortex a flow of air is set upthrough the casing which passes from the inlet 14, twice through thepath of the rotating blades of the rotor 2, through the diffuser 32 andout through the outlet 15. The vortex causes the air to travel throughthe rotor 2 along'lines which are curved about the vortex core V, thegreater part of the throughput being concentrated in the more stronglycurved and faster flow lines adjacent the core. Thus because of thevortex the air is turned through the angle subtended at the rotor by theoutlet 15 and that part of the inlet 14 through which the air chieflypasses, and this turning of the air is unaccompanied -by the losseswhich would occur if it had been accomplished in bent ducting.

An electric heating element 36, comprising a plurality of resistancewires 37 held in castellated insulating supports 38, is mounted withinthediffuser 32 between the guide walls 3 and 4. The wires 37 may becloser together adjacent the wall 3 where the flow is faster.

The guide wall 3 is, as already mentioned, spaced from the interior ofthe casing 1. The space 40 defined between the wall 3 and the casingenables air which has passed through the rotor 2 to return to the entryare thereof, in case the inlet 14 or outlet 15 should be blocked. Theinlet 14 extends over a part of this space 40, so that innormal'operation there is always some air flow through it' from theinlet 14 to the rotor. Within the space 40, and in the air flow justmentioned, there is mounted a thermostat 41 connected electrically withthe heater element 36. By adjustment of the thermostat 41 the heaterelement 36 can be cut in and. out as required to maintain a desiredtemperature in a room in which the fan heater is placed, and will bequick in responding to temperature change by reason of'the air flow overit from the inlet 14 to the rotor 2. Ifthe inlet to cut out the heaterelement.

larger at this side of the outlet duct.

4 14 or outlet 15 is blocked while the heater element 36 is in circuit,the recirculating flow of heated air through the space 40 willimmediately cause the thermostat 41 This arrangement thus obviates theneed for a separate safety switch to cut out the element 36 onoverheating.

FIGURES 3 to 8 show various forms of fan heater unit, i.e. combinationsof rotor, guide walls and heater means, which can be built into a casingof some sort to form a fan heater in the general manner explained withreference to FIGS. 1 and 2, or which can form part of some otherapparatus requiring a stream of warm air. Vertical sections only areshown: the horizontal sections will be similar in principle to that ofFIG. 2. In FIGS. 3 to 8 the reference numerals of FIGS. 1 and 2 will beused for similar parts, which will not require further detaileddescription.

FIG. 3 shows a fan unit where the guide walls 3, 4 carry notchedinsulating support members extending parallel to the rotor axis betweenwhich coiled resistor wire 10 is strung in two layers designated 102,103, which extend obliquely across the diverging outlet duct 32. Byrunning the wire in the manner shown, the heat dissipation of the wiresis greater near the wall 3, where the air velocity is greater since itcomes from adjacent the vortex core region. The resistor wire 101extends over a very large area compared to the cross-sectional area ofthe outlet duct taken in a plane perpendicular to flow. An aperturedcover 104 is supported on the guide walls 3, 4. The guide wall 3 isitself apertured for flow of air between the inlet region and the outletduct 32.

In the arrangement of FIG. 4 the guide walls 3, 4 are formed in twosections providing an outlet duct 32 with an abrupt increase ofcross-section, at which openings 116 are provided. Air flowing in theoutlet duct 32 induces a certain amount of ambient air to flow into theduct through these openings. The air velocity adjacent the guide wall 3is greater than at the wall 4 because of the vortex (flow lines of whichare shown in FIG. 1), and accordingly the injector effect is greateradjacent wall 3. For this reason the openings are A notched insulatingsupport member 111 extends parallel to the rotor within the outlet duct32 midway between the walls 3, 4 in the region of the abrupt increase ofcrosssection. Coiled resistor wire 112 is strung between thesupportmember 111 and two other notched insulating support members 113at the down stream extremities of the walls 3, 4. As in the FIG. 3embodiment, the wire thus extends over a much greater area than thecrosssectional area of the duct 32. a

In FIG. 5 the electric heating element has the form of a textilematerial e.g. woven from resistance wire and insulator filaments, thelatter maintaining the wires in spaced relation. The element 120 issupported on the downstream extremities of the guide Walls 3, 4 and, atleast when the rotor 2 is rotated to set up an air flow, the elementextends like a bag over the outlet end of the outlet duct 32. As shownthe element is formed with folds 121, and the area which is presented tothe air flow is thus once again much greater than that of thecross-section of the duct 32 taken on a plane perpendicular thedirection of air flow in the duct. The divergent part of the guide wall3 is apertured to provide for air flow from the duct 32 into a channel122 formed behind the wall 3 and leading to the motor: in this waycooling air is supplied to the motor.

FIG. 6 shows a further form of cross flow fan with heater. The outletduct 32 is in this case parallel-sided with a constriction at downstreamof the heater element 36 which is mounted obliquely across the outletduct 32 and which in construction is generally similar to that ofFIG. 1. It will be understood from reference to FIG. 1 that the flow inthe outlet duct 32 is fastest adjacent the wall 3 and becomes slowergoing across the duct to the wall 4: this is because in a Rankine vortexsuch as is set up in the rotor onoperation of the fan the fastest streamtubes are adjacent the vortex core V and on leaving the rotor suchstream tubes flow adjacent the wall 3, While going away from the core,i.e. towards the wall 4, the flow becomes progressively slower. Theheater wires 37 are more closely spaced in the region of the wall 3 totake account of the difference in flow speed across the duct whereby,despite this, to heat the air flow evenly. The constriction 130 helps toensure a smooth outlet jet.

In the cross-flow fan with heater shown in FIG. 7, the heater element140 comprises a coiled resistor wire 141 strung between oppositeinsulator members 142, 143 of an open rectangular frame 144. The frame144 is pivoted adjacent the member 143 about an axis close to theextremity of guide wall 4, and can move from a retracted position (showndotted) adjacent the wall 4 to an operative position (shown in fulllines) wherein the frame member 144 lies obliquely across the outletduct 32. The FIG. 7 fan has the advantage that when it is required toproduce a stream of cold air the heater element 140 can be moved to itsretracted position wherein it offers no resistance to flow. A bimetalelement (not shown) can be provided to pivot the heater element 140 intothe air flow under the action of heat developed when the element isswitched on.

As in the embodiments described earlier, those of FIGS. 6 and 7 haveheating elements which extend over an area greater than thecross-sectional area of the outlet duct.

FIG. 8 shows a cross flow fan with a long outlet duct 32 which divergesgoing from the rotor 2 but converges at its downstream end. At thewidest part of the duct 32 is mounted an indirectly heated electricelement 150. When the apparatus is switched off there may be aconsiderable amount of heat stored in the heater element 150. To preventthis heat from damaging the rotor, which may be of a plastics material,a baflle 151 is arranged in the outlet duct 32, which, when the fan isoperating, serves as a flow guide. As in FIG. 6, the convergence of theduct 32 at its downstream end helps to promote laminar flow.

In all the heater elements of FIGS. 1 to 7, it is desirable to ensurethat the size spacing of adjacent wires falls within a particular range.Thus it has been found that the Reynolds number (Re) defined as follows:

should be below 60. FIG. 9a shows purely diagrammatically a wire 160 ofa heater element in an arrange ment where the Reynolds number is wellbelow 60: flow is more or less laminar. At a higher Reynolds number,shown in FIG. 9b, flow conditions are slightly disturbed, where theReynolds number greatly exceeds 60, as shown in FIG. 90, the conditionsare turbulent and energy is wasted in random eddies, resulting inreduced throughput and an outlet jet of impaired penetrative power. Itis also necessary to space adjacent wires by substantially more than thewire diameter since otherwise the boundary layers of the wires mergeinto each other and the element becomes virtually impermeable.

FIGURES 1 to 8 do not show the specific means by which the rotor 2 isrotatably mounted. One form of such means is illustrated in FIGURE 10;parts shown in FIGURE 10 which are similar to those of FIGURES l and 2are designated by the same reference numerals and will not need furtherdescription.

The rotor 2 comprises a series of blades 200 extending parallel to therotor axis and arranged in a ring thereabout to define an unobstructedinterior space, the blades 200 being mounted on rotor end members 201,202 of sheet material and generally of disc formation. The driven rotorend member 201 is coupled to the shaft of the drive motor 19 by a driveconnection 203, and the end member 202 at the nondriven end of the rotor2 is rfotatably mounted from the stationary end' wall 6 of the The driveconnection 203 comprises a flexible ring or bushing 205 preferably madeof soft rubber and having a central portion of reduced thickness whichengages a portion 206 of reduced diameter on the shaft 20 of the drivemotor 19. The drive 205 has a grooved periphery 208 which grips theopposite faces adjacent an aperture 209 in the rotor end support member201. Lugs 211 integral with the ring 205 and projecting therefrom arearranged to engage in pin 212 secured to the shaft 20 to rotate therotor 2 upon rotation of the shaft. To reduce the axial length of therotor the end support member 201 is inwardly dished.

By providing suificient frictional engagement between the ring 205 andthe portion 206 of reduced diameter on the shaft 20 the lug 211 and pin212 can be dispensed with.

The supporting means 204 for the other end of the rotor 2 comprises astub shaft 214 rigidly secured to the rotor end member 202, a flexiblegenerally conical diaphragm 216 secured at its thickened periphery bymeans of rivets 217 to the wall 6 and a bearing 219 secured to thecentral portion of the diaphragm 216, the stub shaft 214 beingjournalled in the bearing 219. The central portion of the rotor endmember 202 is inwardly dished at 220 and the stub shaft 214 is securedto this dished portion, which accommodates most of the axial length ofthe diaphragm 216, stub shaft 214 and bearing 219 thus reducing thedistance between the end of the rotor 2 and the mounting plate 6. Thediaphragm 216 is, in this embodiment, made of rubber with the centralportion of increased thickness at 221, this central portion having arecess 222 into which the bearing 219 is fitted. A cylindrical bore 223of the bearing 219 receives the stub shaft 214, which has a sphericaldepression for receiving a ball 224 located in the closed end of thebore 223 to provide an end limit stop for the shaft 214.

The ring or bushing 205 and the diaphragm 116 are both capable ofaccommodating substantial universal movement without imposing brakingtorques, and thus minor misalignments of rotor 2, drive shaft 20 and endwall 6 will not interfere with the proper operation of the fan.Moreover, both the diaphragm 216 and the ring or bushing205-particularly when the lugs 211 and pin 212 are omittedcanaccommodate also appreciable variation in the axial spacing of theparts. The diaphragm 216 can also compensate for a minor degree ofeccentricity or misalignment of the stub shaft 214 relative to the trueaxis of the rotor. Thus the rotor 2 is mounted in a manner whereby evensubstantial inaccuracies of manufacture, such as may occur in economicquantity production, do not affect the successful operation of the fan.

Moreover, it will be seen that the rotor mounting arrangement describedpermits the rotor to be assembled within the guide wall structure bysimple manual manipulation after insertion of the rotor through the wideopening between the guide walls 3, 4 on their inlet side.

FIG. 10 shows a further important feature of the invention which is theformation of a circular recess 230 in the end wall 5 within which islocated the end disc 101 of the rotor 2, the surfaces presented to airflow by the wall 5 and the end disc 101 being flush with one another.This arrangement, which can also be adopted at the other end of therotor, reduces the disturbance to air flow and improves the operation ofthe fan.

I claim:

A fan heater comprising: a casing having an inlet and an outlet; abladed cylindrical rotor within the casing said rotor defining aninterior space; means mounting the rotor for rotation about its axis:drive means to rotate the rotor in a predetermined direction; guidemeans comprising a pair of end walls in substantial alignment with theends of the rotor and a pair of spaced guide walls extending generallyparallel to the rotor axis between the end walls, said guide meansdefining an entry region communicating with the inlet and a dischargeduct leading directly to the outlet, the guide means and rotorcooperating on rotation of the latter in said predetermined direction toinduce a flow of air from the entry region through the path of therotating blades to the interior space and thence again through the pathof the rotating blades to the discharge duct, heater means including anelectric resistor element mounted within the discharge duct, meansforming an air by-pass passage Within the casing between .the dischargeduct and the entry region, and a thermostat effective to control currentsupply to the resistor element, 15

the thermostat being located in the entry region and in the path of airflow from the discharge d-uct through said by-pass passage on blockingof the outlet.

References Cited by the Examiner UNITED STATES PATENTS 1,626,400 4/ 1927Frank. 1,679,841 8/1928 Shaw 219-375 X 1,823,579 9/1931 Anderson. 11,920,952 8/1933 Anderson. 2,458,268 1/1949 Hinds 219370 X 2,822,6742/1958 Simmons. 10 2,988,626 6/1961 Buttner 219375 X 3,035,760 5/1962Simmons.

FOREIGN PATENTS 757,543 9/1956 Great Britain.

ANTHONY BARTIS, Primary Examiner.

